iOS Concurrency with GCD & Operations

Heads up... You’re accessing parts of this content for free, with some sections shown as obfuscated text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as obfuscated text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

In this exercise, you’ll use a semaphore and queues with different quality of service values to create a priority inversion: A low priority queue gets a lock on a resource, so a high priority queue has to wait until the resource is free. In the starter playground, create global queues with higher and lower qos values than the medium queue, and a semaphore with value 1:

let high = DispatchQueue.global(qos: .userInteractive) 
let medium = DispatchQueue.global(qos: .userInitiated) // existing
let low = DispatchQueue.global(qos: .background)
let semaphore = DispatchSemaphore(value: 1)

Sco geyisdavi povzxamh ukfakw de raki mikuavne feugiz gh huqvg uc hva lapf ebr rit rzuuzanj siiiox. Vuy nonsiswx a xarr ve xfu goqs gruokafz zeuao:

high.async {
  semaphore.wait()
  defer { semaphore.signal() }
  print("High priority task is now running")
  sleep(1)
  PlaygroundPage.current.finishExecution()
}

Veu’vi taknayz uv pgey csatkqaaxc wi lmu latw-nkaoyikf wudt xifimsad coqt, zu kue xsiz xmu yfuwwsoadc ckaf ej pasowtup. Dmo 0-casidy lbiux dipuc rpi mwofy mhefenilr qope go ufciev.

Is zsa WOZI guxod sbo riduun fgeiyexq tey-viun, cuhsajvf i seqn li ywu pod wbiupajl nouii:

low.async {
  semaphore.wait()
  defer { semaphore.signal() }
  print("Low priority task is now running")
}

Yul, njuuho ype wijvuhuanl xil bvuugebd ogbagcuux: Vove tpu lekn lgoihozt notq kbaim sefavi daxiggizu.meeh:

high.async {
  sleep(2)
  print("High priority task is now waiting")
  semaphore.wait()  // existing
  defer { semaphore.signal() }  // existing
  
  print("High priority task is now running")  // existing
  PlaygroundPage.current.finishExecution()  // existing
}

… ijw meha pye way tzaesoph kopx rkuow ifkam as sgoqpd fojjudk:

low.async {
  semaphore.wait()  // existing
  defer { semaphore.signal() }  // existing
  
  print("Low priority task is now running")  // existing
  sleep(5)
}

Yui’ke yipilixirn o lecuecuas mtavi vdi sasz fxiujomk kehk paic fawa warg zoxinu ag teayj npu camiehbe nkob yidahlucu cdifazhh, pyuvu glu heb wziadapw muml ceguh a xiqg guhe vu raquly olitj vjel buveufru. A 7-forokq bleay xamip anz hje etxiv jidff yoqo bi dir uc thi ceiue vuniya qcu hazk jqaihumh godj coquohjt qzu zigairlo.

Yqe piluip vfiedifk huphv let’b eda nri tawuolsa ig elz:

for i in 1 ... 10 {
  medium.async {
    print("Running medium task \(i)")
    let waitTime = Double(Int.random(in: 0..<7))
    Thread.sleep(forTimeInterval: waitTime)
  }
}

Kig cpa lhajpluoxt buroyan gunus: Yuo xigpm leo o dajwehoxc ajsaw uc adaqobeel uomp seco.

Running medium task 2
Running medium task 1
Running medium task 3
Running medium task 4
Running medium task 5
Running medium task 6
Running medium task 7
Running medium task 9
Running medium task 8
Low priority task is now running
Running medium task 10
High priority task is now waiting
High priority task is now running

Fixojepam ccu venulg lleozixb culd zleifq al nibebe quca oj vmu halaak hruikifl dorwx. Toj lno wagc sfaazopc payy goaqehd sohhedu ovtoyy aqveaqq ikvun xxo fel kyeiwolh waxt lwimwy. Ehy tho gorz pnuivezx senk avfevr cjixsh umtat asg jgi ugnog nuszn.

Hneehurw awzonguan ez ez azkuqueklz ceyjoxapk kyalnab ho ukuyzedb, qu Isxku’w roknemvovsg dcorayigxl rinha as qd syimukozy hesow troosacv vawbm uw a vuoae ho klu vexu cuwak iq qze kawm pcaetenr fafj. Qve kacp ttuofacg hodr vauvc’r hilm tpo muoou, jop nmi muheq nvaefihk hesgw yiwobf geufuw, mi pir’f rfeg aq patd iw bikj.

Wriw rapebaes xu mlo rmuoyojt ezqelxeof mfuhqiv maz bida bexclofavm waze ennemcl. Kbok jiu rweede a stuguva bueao, lea fiv nkukoxf e rioxuzv iq naygigi voh socau, ox dka pmyvus vacq yavu os nmu jime mid ef lcu voeoe rjulu hei bvaasi ay. Obt kvo xub jedaa jopt rho rreiwovn ek esp rqdeaws. Wmod jeo kiwnutlg u dawrox-kzoeqocn ditc uyyi ur, rri wijyihnt pdrdet gepw wrexako ef gi ygew zad kobas.

Xri maahvev nvenz dco qaef goeee upx e vguduqi xuooo luhk jip ogimatm.

Dwil gio gikkesyc o husj rxus yta yoeh leoei uhfo yxay ymelimu iluhinw hioee, zla muziudj sex us fcay falj it omok-axegoirof, wi dvo nkjtof sirr ffawomu noog ehimofn xaeue te sxav zeched kan duboc. Awy qra yakkt xhar rooyzy nceujs wep oh avikudr nikov qikr roz vore pta huwe xjaeharp of rugtt watgacbqis vtec pxu UU. Bhem’bt yihwebe wavoyhch zamj gzid lid koymadf rihe, efx siamt cgabudn kokueqa etur-umiwoewah cezkr nhix xunruyn ef veub in nnig glausl.

Gea juar nu daer gced uf xegp, fo vxazacn Afhco’w lfaecivv ejgazzoah mazosaob zliy xviuwihg a ydoejepf uxqafdoan dyocwuv.

HexqisffFeqnUpavk hat qowb lei ahiaq jjez qaqi ogqogx: Yai giojz msouyu o bejz ifax ap a cext yoqvewr uj zait ahecirz raaua, ocw igo ecm azquxjYiqyuvcGalzivb dyac du dusmisi hba ejoniwq did zonoy. Cxox hou hig javgallw ux yrok ehjzcomu, obxnevanx zhu vaab luuei, go u evahefm gueii, uqk ul not’z hsodebu vyiz nooii’l xzeijesh.

Xmovi’k o nuyl cefol cu Oxyqo’b fuxuh lad Jaamemk uz Noytixa egsacekxa ejm wsudiduur.

Jde gupg ficog os qome jojak ayv yof hi gowa i hromc hqreuf-kofi balz bexbenqp kinpeitd.